‘With an oustiti,’ nodded the Sergeant. ‘That’s what I was thinking. Only there aren’t any scratches on the key. If it weren’t for that, I’d say an oustiti must have been used.’

‘That, and about half a dozen other reasons,’ interrupted his superior scathingly. ‘You aren’t dealing with a professional burglary, my lad: this is an amateur-job; and whoever heard of an amateur having a tool out of a professional’s kit?’

‘I thought of that, but I don’t know but what he might have come by it,’ argued the Sergeant.

‘He might, but the odds are he didn’t,’ retorted Hemingway. ‘Not one layman out of a hundred would know there was a tool for turning keys from the wrong side, let alone the name of it.’

‘Most people know there is a tool for doing that,’ persisted the Sergeant. ‘I don’t say they’d know the name, but –’

‘No; they’d just walk into the nearest ironmonger’s and ask for a pair of forceps shaped a bit like eyebrow-pluckers to open locked doors with, I suppose,’ said Hemingway, with awful sarcasm.

The Sergeant reddened, but said: ‘Well, that’s an idea, anyway. Suppose the key was turned with a pair of eyebrow-pluckers?’

‘I’m not going to suppose anything of the sort,’ replied Hemingway. ‘For one thing, they wouldn’t be anywhere near strong enough, nor pliable enough; and for another, the grooving on them would be horizontal, instead of vertical, and wouldn’t give them any grip on the key. Try again!’

‘Well, sir, it’s all very well, but if an oustiti wasn’t used, what was? The murderer got into the room somehow. That we do know. Or if the door wasn’t locked before the murder, it was after, and there’s no sign the key was turned by the old pencil-and-string trick. It beats me.’

‘You’re a great help,’ said Hemingway. ‘Ever asked yourself why the murderer took such precious care to lock the door after him?’

The Sergeant considered this. ‘I hadn’t thought of that,’ he admitted. ‘Now you put it to me, sir, it does seem queer. Doesn’t seem to be any point to it at all, unless it was just done to bamboozle us.’

‘Which it probably was,’ said Hemingway. ‘And I’m bound to say it’s succeeding up to the present.’

‘Bit of a risk to take, wasn’t it? Fiddling about with a door-lock when anyone might have seen him?’

‘Whoever committed this murder took the hell of a lot of risks, if you ask me. If I remember rightly, Miss Herriard was seen outside the door in her dressing-gown.’

‘You don’t think this was a woman’s job, sir, do you?’ asked the Sergeant incredulously.

‘Might have been. Don’t you go getting a lot of silly ideas into your head about women! I’ve known some who’d have put a cageful of tigers to shame. One thing seems pretty certain: Nathaniel wasn’t expecting to be stabbed. There are no signs of any struggle, not even a chair pushed out of place. He was taken unawares, and he didn’t suspect the murderer of meaning to injure him.’